BACKGROUND: The inner surface and capsule of joints are lined by a delicate vascular connective tissue known as the synovial membrane. In rheumatoid arthritis and related conditions, the membrane may become massively inflamed and thickened. OBJECTIVE: The objectives of this study are to characterize these tissues in terms of the molecular mediators involved in generating the pathologic change. Our most recent studies have been focused on synovial specimens from a subgroup of patients with Chlamydia-associated arthritis who were not treated with second-line drugs or corticosteroids. RESULTS: We completed our analyses on the synovial samples from the patients with Chlamydia- associated arthritis. All of the patients had very high levels of both gamma interferon and IL-10 relative to our control groups with other diagnoses or normal control synovial tissues. We have speculated that the high levels of both a type 1 and type 2 cytokine may favor persistence of the organism in the joints. A manuscript describing these findings was submitted and published. CONCLUSIONS: Inflammatory synovitis, in its earliest stages, represents a very heterogeneous group of clinical disorders. They appear to have variable genetic influences, environmental triggers, pathogenic mechanisms and responses to therapy. Chlamydia-associated early arthritis appears to be very common. Our studies provide potential insights into factors that may influence the chronicity of this condition and may ultimately lead to new approaches to diagnosis and therapy. These patients provide an excellent contrasting control group for patients with other forms of arthritis, such as rheumatoid arthritis. - rheumatoid arthritis, synovitis, arthritis, cytokines, chlamydia - Human Subjects